1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor laser device having a ridge portion. In the invention, a term “substantially perpendicular” includes “perpendicular.”
2. Description of the Related Art
Semiconductor laser devices, for example, AlGaInP red semiconductor laser devices that oscillate at 600 nm band are used as a light source for optical information processing of a pointer, a bar code reader, a laser beam printer, an optical disk and the like. Semiconductor laser devices such applied are required to emit a higher power laser beam and with increasing the laser beam power exhibit capability of high-temperature operation even in a high-temperature environment, for example, in order to realize increase of writing speed into an optical disk. A real refractive index guided laser having a dielectric ridge embedded structure is effective in manufacture of a high power laser. Hitherto, a method for manufacturing a semiconductor laser device of dielectric ridge embedded structure has been practically used (refer to Japanese Unexamined Patent Publication JP-A 2002-198614).
FIG. 5 is a sectional view showing a semiconductor laser device 1 manufactured by a conventional method for manufacturing an AlGaInP red semiconductor laser device 1 of the dielectric ridge embedded structure (hereinafter, may be simply referred to as “the method for manufacturing the semiconductor laser device”). FIG. 6 is a sectional view showing a work in step where a ridge portion 2 is formed in the conventional method for manufacturing the semiconductor laser device 1. FIG. 7 is a sectional view showing a work in step prior to removal of part of the ridge portion 2 in the conventional method for manufacturing the semiconductor laser device 1. In the method for manufacturing the semiconductor laser device 1, firstly, an n-type GaAs buffer layer 4, an n-type GaInP buffer layer 5, an n-type AlGaInP cladding layer 6, a GaInP/AlGaInP multiple quantum well active layer 7, a p-type first AlGaInP cladding layer 8, a GaInP etch stop layer 9, a p-type second AlGaInP cladding layer 10, a p-type GaInP intermediate layer 11 and a p-type GaAs cap layer 12 are sequentially laminated on an n-type GaAs substrate 3. Subsequently, part of the p-type GaAs cap layer 12, the p-type GaInP intermediate layer 11 and the p-type second AlGaInP cladding layer 10 is dry-etched, and UV-O3 ashing is performed for the purpose of oxidizing adherents adhering to the surface of crystal after etching.
Subsequently, the p-type GaAs cap layer 12 is side-etched with an etching solution of a sulfuric acid and hydrogen peroxide solution base. Then, as surface treatment for stably performing the following etching, immersion into buffered hydrofluoric acid is performed to rinse. Subsequently, the p-type second AlGaInP cladding layer 10 is wet-etched until etching stops on the GaInP etch stop layer 9 to form the ridge portion 2. As shown in FIG. 6, the ridge portion 2 has a protruding portion 13 formed into a visor shape of the p-type GaInP intermediate layer 11.
Subsequently, a resist 14 is applied, instant exposure is exposed, only a part on one side in a lamination direction from the p-type GaInP intermediate layer 11 of the ridge portion 2 is exposed as shown in FIG. 7, and etching is performed by using the resist 14 as a mask, whereby the protruding portion 13 is removed. As an etching solution therefor, a mixture of phosphoric acid, hydrochloric acid and a hydrogen peroxide solution is used.
Subsequently, a dielectric film, for example, a SiO2 film 15 is evaporated on the outer peripheral portion of the ridge portion 2, and the SiO2 of one end portion in the lamination direction of the ridge portion 2 is removed by etching by photolithography. At last, electrodes 16, 17 are formed on both the end surface portions in the lamination direction, respectively, whereby the AlGaInP red semiconductor laser device 1 having the dielectric embedded ridge structure as shown in FIG. 5 is obtained.
FIGS. 8A to 8C are sectional views showing states where abnormalities occur in the case where part of the ridge portion 2 is removed in the method for manufacturing the semiconductor laser device 1, FIG. 8A is a sectional view showing a state where the p-type GaAs cap layer 12 is removed undesirably, FIG. 8B is a sectional view showing a state where the p-type second AlGaInP cladding layer 10 is etched undesirably, and FIG. 8C is a sectional view showing a state where the base of the protruding portion 13 is not removed undesirably.
The method to remove the visor-like protruding portion 13 of the p-type GaInP intermediate layer 11 by etching using the mixture of phosphoric acid, hydrochloric acid and a hydrogen peroxide solution in the prior art has the following problem. There are fears that the p-type GaAs cap layer 12 is lost as shown in FIG. 8A, and that resulting from damage of the resist 14 by the etching solution, the etching solution penetrates from a gap of the resist and the p-type second AlGaInP cladding layer 10 is etched as shown in FIG. 8B.
Further, as another method for removing the protruding portion 13, there is a method to physically remove by, for example, giving ultrasonic vibrations to the protruding portion 13 by ultrasonic washing and breaking the protruding portion 13. In this method, there is a fear that the protruding portion 13 is not removed from the base as shown in FIG. 8C, and it is impossible to completely remove the protruding portion 13.
In the case where the p-type GaAs cap layer 12 and the p-type second AlGaInP cladding layer 10 are etched undesirably as described above, when the p-type GaAs cap layer 12 is partially lost, there is a fear that the electrode is formed so as to come into contact with not the p-type GaAs cap layer 12 but the p-type GaInP intermediate layer 11. Thus, there is a problem such that the electrode cannot be appropriately formed, resistance increases, and an operation voltage increases.
In the case where the protruding portion 13 is not completely removed, namely, in the case where a smooth ridge is not formed after removal of the protruding portion 13, a part right under the protruding portion 13 is shaded and the dielectric film 15 is not evaporated. Therefore, the ridge portion 2 cannot be satisfactorily embedded by the dielectric film 15, so that there is a problem such that light leaks out of the not-evaporated part, external differential efficiency decreases and the value of an operation electric current increases.